I also got Cheng's book on his form, and made some adjustments from there, and watched the videos of him and other people practicing his form. I also got Yang Cheng Fu's book on the traditional form. I met someone who practiced Cheng's form and practiced with them briefly, I picked up some things from him. I didn't try to understand or salvage the way CSC taught me, my assumption was that the differences were mostly mistakes made in interpreting what had been learned (on the part of me, my teacher, and all the way up to Sin The), and I changed my practice to the more conventional Yang way, taking guidance from the texts and videos to correct me. The diagonal single whip is just a regular single whip except for the direction you're pointing relative to the starting position. I think it's application is the same as all single whips, since your feet and body move in the same manner relative to your starting position with the push to the northwest: you turn 180 degrees and end up with a single whip to the southeast.
I found the video below very useful for getting some details in the Yang style long form, much of which is identical to the sequences CMC used. Of course there are also postures in the long form which are also found in the simplified 24 postures, if you still practice it, and I've changed how I pratice those as well, such as the "wave hands in clouds" that I originally used replaced with fan through the back, and correcting how I do chop with fist and deflect, parry and punch (aka plant hammer under the sleeve). It actually isn't hard to pick up the long form with the content of both CMC's form and the 24 form under your belt. There are only a few postures not found in either form.
It is a five hour seminar, and it covers details of the entire form. I think Yang Jun's (the grandson's) demonstrations are pretty stiff (maybe he's doing it on purpose for demonstration purpose), I just skipped over those parts, but Yang ZhenDuo goes into great detail during his explanations.
Part2 starts with embrace tiger return to mountain, he explains it at 3:52. It really is pretty simple, as I understand it. The pictures in the books make it hard to see. When I saw my friend do it, I asked him about it and he said it is just like a brush knee and press but stepping back and turning from the south to the northwest, followed immediately by a rolling back. That's what the video shows, too. There is an arm grab application in the transition from the brush knee to the roll back. My interpretation of the photo of that posture shown in Cheng's book is that it is describing the intermediate stage between the brush knee and press and the rollback, which is really the only different thing about it, where the lower hand has just turned palm up and is about to rise up for the grab and roll back.
http://www.youtube.com/watch?v=kUnXFvDeGII
http://www.youtube.com/watch?v=tNa-Y2AkII8
http://www.youtube.com/watch?v=1wptDgG4IvU